Cutting articles and stock therefor and methods of making the same



United States Patent 3,313,660 CUTTING ARTICLES AND STUCK THERE- gOR ANDMETHQDS 0F MAKENG THE AME Milton 3. Vordahl, Beaver, Pa, assignor toCrucible teel Company of America, Pittsburgh, Pa., a corporation of NewJersey N0 Drawing. Filed July 15, 1963, Ser. No. 295,234 12 Claims. (Cl.14811.5)

This invention pertains to cutting blades, especially razor blades, andmetal stock therefor and to methods of manufacturing the same, andparticularly to such articles comprising a high hardness central coreand overlying layers of a relatively softer composition.

Very thin gauge cutting articles, such as razor blades, are commonlyconstructed of high carbon steels containing, for example, 1.2 to 1.4%carbon, balance substantially iron. Such steels do not cut as eficientlyor wear as well as many other steels, such as alloy tool steels, but thelatter are much too diflicult to roll to the required thin gauges. Eventhe high carbon steels, as aforesaid, generally used for the manufactureof razor blades, are difficult to mechanically reduce to the requiredextent. Best cutting ability is attainable with materials such as veryhard carbides, as the carbides of titanium, tungsten and the like, butsuch materials are extremely brittle and impossible to produce in sheetform. However, such carbides are frequently utilized in the productionof cutting tools by powder metallurgy techniques. For example, suchcarbides are commonly ground to the form of a fine powder and dispersedin a softer matrix metal, which mixture is then cast into the desiredshape. Even such cast articles cannot be mechanically reduced, as byrolling, to thin gauge forms. It is known to the prior art to providecutting tools as blades and the like with inserts of cast carbides,which are then ground to a relatively fine edge. Such cast materials,however, in view of their relatively high content of the extremelycarbide particles are susceptible to easy chipping and breakage.

Prior art attempts to utilize the beneficial eifects of hard carbides inthe production of cutting tools include mixing preground carbide powderswith a softer metal matrix, such as a low melting point, ductile metal,for example, copper, nickel, cobalt, tin, lead, zinc, antimony orbismuth, pressing the mixture by powder metallurgy techniques to theform of a billet, sawing blanks from the billet and grinding the blanksto the desired cutting edge, and then aflixing the ground blank, bysuitable means such as welding, soldering or brazing, to a suitablebacking material. The disadvantages of such procedures and the articlesproduced thereby are many and varied. For example, the fineness of theedge obtainable by grinding a carbide-containing metal, and the cuttingefiiciency of the article, are dependent upon the carbide particle sizeand the uniformity of dispersion thereof in the matrix metal. Theparticle size obtainable by mechanical size reduction of carbidecompositions is limited, as is also the homogeneity of dispersion whensuch ground powders are mixed with the matrix metal in either moltenform or in the form of similarly preground powder. Moreover, thegrinding, mixing and compressing steps required in such prior artprocesses are'time consuming and expensive. Additionally, the mechanicalsteps inherent in assembling a laminated article, such as a cuttingblade, from two or more laminations comprising a carbide-containingmaterial are also expensive and are unsuitable for articles of extremelythin overall gauge such as razor blades.

Other attempts have been made by the prior art to produce thin gaugearticles, such as razor blades, by methods and means whereby thedifficulties inherent in the blade,

reduction of relatively brittle material such as high carbon steel areavoided, or whereby the fragility of the final product, due to itsinherent brittleness is overcome. For example, nitriding metal stock hasbeen rolled to final gauge, cut to the desired article shape, ground toa cutting edge and the article then case nitrided to produce a veryhard, wear resistant cutting edge. However, such articles cannot bereground because such an operation would destroy the hard nitrided case.Cutting articles have also been prepared by nitriding one side only of aand the blade then sharpened by bevel grinding. Such articles areunsatisfactory because the hard, nitrided edge is unsupported on oneside and tends to easy chipping in use. Articles such as cutting bladeshave also been prepared by assemblying laminates of a plurality oflayers wherein an inner layer comprised a hard suitable cutting materialoverlain with relatively softer, more resilient materials.

Such articles are, indeed, more resistant to breakage during use due totheir enhanced resilience, but the dir'iiculties in manufacturing sucharticles are still formidable. Thus, it is still necessary to reduce thecentral layer of hard cutting material to very thin gauge form.Moreover, such laminated products, if joined by usual techniques such aswelding, soldering or brazing, are not suited for production ofextremely thin gauge articles such as razor blades. It is also known inthe prior art to utilize carbides in ferrous matrices, by electroplatingand infiltrating loosely pressed compacts of carbide particles withmolten steel. The disadvantages of such processes and theinapplicability thereof to the production of thin gauge articles areself-evident.

Accordingly, it is an object of the invention to provide cutting tools,in the form of thin gauge articles, such as razor blades, which haveenhanced cutting ability, wear resistance and resilience, and therebyhave increased eifective lives.

It is a further object of the invention to provide a thin gauge, cuttingblade having superior cutting properties and amenable to repeatedregrinding.

It is another object of the invention to provide unitary stock for themanufacturing of cutting blades and having a central core of hardmaterial for forming a cutting edge and juxtaposed to and integrallyunited with overlying layers of relatively more ductile, tough andworkable material.

It is still another object of the invention to provide thin gaugecutting blades, and stock therefor, comprising a multilayeredcomposition having a central layer containing fine particles ofhomogeneously dispersed carbides.

It is yet another object of the invention to provide methods forproducing the articles as aforesaid.

It is a still further object of the invention to provide articles, ascutting blades, and stock therefor comprising a matrix metal of arelatively ductile, workable metal having dispersed homogeneouslytherethrough fine particles of hard carbides.

It is another object of the invention to provide methods for producingarticles such as cutting blades and the like, and stock therefor,wherein the article or stock comprises a metal cold rollable torelatively thin gauges and which contains a homogeneous dispersion offine particulate carbides.

It is another object of the invention to provide methods for producingarticles such as cutting blades and the like, and stock therefor whereinthe article or stock comprises a metal cold rollable to relatively thingauges and which contains a homogeneous dispersion of fine particulatecarbides.

The foregoing and other objects of the invention will be more readilyapparent by reference to the following description.

As indicated above, the value of hard carbides such as those of tungstenand titanium as cutting materials is appreciated by the prior' art, asis also the similar value of other carbides such as those of columbium,tantalum, zirconium, hafnium and vanadium, and, indeed, some of thesematerials have been incorporated in preground powder form in variousmetallic matrices and fabricated by various methods into cutting tools.The known advantages of such carbide materials, for incorporation incutting tools, are utilized, while the aforementioned, importantdisadvantages accompanying the production and use of such prior artarticles are overcome, by the present invention which provides a unitarycutting article having the cutting edge thereof consisting of adispersion of extremely small carbide particles in a matrix of arelatively tough, workable, ductile metal.

Such articles are provided by the expedient of in situ formation of thedispersed carbides within the matrix metal, in a restricted zone thereofconstituting the ultimate cutting portion of the blade.

7 The cutting ability and efficiency of a tool comprising a matrix metalcontaining dispersed carbides is a function of the type of carbide, thequantities thereof present and the homogeniety of dispersion thereofwithin the matrix metal, as well as, quite importantly, upon the size ofindividual carbide particles. Thus, the cutting ability and the keennessto which the cutting edge of a carbide-containing blade can be sharpenedis directly dependent upon the fineness of the carbide particles. Acommon defect of prior art carbide-containing compositions, drasticallylimiting their utility in the construction of fine-edged blades, asrazor blades, knife blades and the like, has been the difficulty, and,indeed, the impossibility, of reducing the preformed carbide powders tothe necessary, extremely small dimensions and of uniformly dispersingthe powders throughout the matrix metal, without obtaining undesirablylarge agglomerations of the fine powder particles. It has alsoheretofore been difiicult or impossible to homogeneously dispose finecarbide particles within a restricted portion of the matrix metal of anarticle or stock therefor.

Now, however, by application of the principles of the present invention,carbide particles of small size may be incorporated in a desired matrix,in a homogeneously dispersed form, and, moreover, may be restricted to aparticular, desired zone of the matrix metal, thereby enabling theproduction of a unitary article having a cutting zone ofcarbide-containing metal, juxtaposed to and forming an integral unitwith further zones of substantially carbidefree metal. The advantagesinherent therein are obvious, as compared to prior art articles andmethods requiring prior production of carbide material, grinding of thesame, intermixing with matrix metal to form a cutting composition andthen fabrication thereof as by welding, brazing, etc., with additionallaminations of carbide-free metal.

Illustrative of the invention is the production of cutting tool bladesand metal stock therefor wherein the cutting portion thereof comprisestitanium carbide. Thus, a laminate is made comprising a central layer oftitanium sheet or foil and juxtaposed upper and lower sheets of lowcarbon steel, e.g., AISI 1010 carbon steel, containing 0.08- 0.13 weightpercent carbon. This laminate is then hot rolled to bond the severallayers together and to reduce the thickness to nearly the desired finalgauge. The hot rolled product is then diffusion annealed to form atitanium-iron alloy layer, e.g., about 2 mils in thickness. The annealedarticle is then carburized, by suitable means, and for a sufficient timeand at a sufiicient temperature, to substantially increase the carboncontent in the steel layers. Thereafter, the carburized article issubjected to a further diffusion annealing step whereby carbon from thesteel sheets is diffused into the titanium core to react therewith,forming discontinuous, homogeneously dispersed titanium carbideparticles. The article is then subjected to a partial decarburization toremove excess carbon from the steel sheets, for example, to removetherefrom substantially all carbon remaining in the steel over and abovethat originally present. The decarburization step may be carried out inany suitable manner in accordance with well-known prior art principlesFor example, the carburized article may be subjected to the action ofwet hydrogen. In view of the relatively slow decomposition of titaniumcarbide, control of the decarburization process to stop short ofcomplete carbon removal is easily accomplished. The partiallydecarburized article is then cold rolled to a desired final thickness.Blanks, in the shape of the desired final article, as a cutting blade orthe like, are then cut from the rolled stock and an edge, constituting acutting edge, is ground by any suitable means.

In the case of some articles, particularly those comprising matricescontaining the more reactive alloying elements, as chromium, there issome tendency toward surface and immediate sub-surface oxidation duringthe decarburization step. Therefore, it may be desirable andadvantageous, before cold rolling such surface decarburized articles, tosubject the same to a vacuum annealing treatment at time, temperatureand pressure sufficient to remove surface and trace internal oxidationto a depth of about 1 mil, Without, however, deleteriously affecting thelaminar distribution of carbon or carbides in the article. Such objectscan be accomplished, for example, by utilizing an anneal at atemperature of at least about 1500" but not over about 200 F., at apressure less than about 50 microns of Hg for a time of at least aboutfive minutes. The length of time of such heat treatment can, of course,be varied depending upon the severity and the depth of internaloxidation of a particular product. Similar treatment with dry hydrogen,for example, maximum moisture content not over about 25 microns partialpressure (e.g. dew point-40 to 60 F.) at atmospheric pressure, can besubstituted for vacuum heat treatment if desired.

Exemplary of the aspect of the invention hereinabove described, titaniumfoils of 5 mil thickness were inter posed between (1) sheets of A1511015 steel (0.12 to 0.18% carbon, 0.30 to 0.60% manganese, 0.04%phosphorous, 0.050% sulfur, balance substantially iron), and (2) sheetsof AISI 304 stainless steel (0.08% carbon, 2.00% manganese, 0.045%phosphorous, 0.03% sulfur, 1.00% silicon, 18 to 20% chromium, 8 to 12%nickel and the balance substantially iron). All of the steel sheets wereof 30 mil thickness. In each instance, the above-described laminateswere edge welded with A181 1015 steel and rolled to a thickness of 10mils. The rolled products were then annealed in vacuum (although anyinert atmosphere could be used) for six hours at 1800 F.2000 F. (or ashigh as possible without formation of a eutectic liquid at the interfaceof the matrix metal and titanium) in order to effect diffusion of thetitanium interlayer into the juxtaposed steel layers to produce acentral zone of iron-titanium alloy. Late in the diffusion process thetemperature may be raised above 2000 F., to enhance diffusion rate,especially in the case of thicker articles. This temperature limitationdoes not apply in the case of the use of carbide formers in the form ofhigh chromium, tungsten, molybdenum or vanadium alloys which do not tendto form such lowtemperature eutectic compositions. It is essential, forthe purposes of the invention, that the carbide-forming interlayer bethoroughly alloyed with adjacent portions of the matrix metal in orderto avoid a sharp interface with the matrix metal, inasmuch as such aninterface would tend to cause separation. Such diffusion of thecentrally disposed, carbide forming layer should not, however, becarried to an extent as to destroy a discrete carbide-forming centerlayer. Such precaution in avoiding destruction of the carbide-formingcenter layer is, of course, unnecessary except in the case of extremelythin articles, as razor blades, since, with the slow diffusion ratesinvolved, even relatively prolonged heating of thicker articles wouldnot deleteriously affect the central layer. Thereafter, the articleswere carburized by heating the same for one hour at 1800 F. in a naturalgas atmosphere containing a small percentage of oxygen to deposit a thinfilm of carbon on the surfaces of the products. The carburized productswere then partially decarburized by heating for one hour at 1800 F. inwet hydrogen (70 F. dew point). Examination of the decarburized productshowed a central region having a high concentration of titanium carbideparticles ranging in size from about 1 to about 50 microns and dispersedin a matrix of the overlying metal.

It will be obvious to one skilled in the art that other strongcarbide-forming materials than titanium may be substituted for the corelayer of the initial laminate in accordance with the foregoingdescription. Thus, the core layer may comprise zirconium, columbium,tantalum, hafnium or vanadium. Chromium, tungsten or molybdenum may alsobe used. Alloys of any of these elements, or combinations thereof, maybe used. Any suitable, desired base metal may be utilized in theproduction of such alloys for use as core layers in the contemplatedlaminated raw material.

Further, a wide variety of materials are useful as outer layers for theaforementioned laminates. Thus, high carbon steels may be used, incombination with a core layer of any one or more of the aforementionedcarbideforming elements or alloys therein. High carbon steels have thedisadvantage of exhibiting considerably higher resistance to rolling tothin gauge form than the lower carbon steels. However, high carbonsteels, e.g., AISI 1025, containing 0.22-0.28 percent carbon, are usefulin that, by the use of such higher carbon steels, the carburizing stepcan be omitted and reaction with the carbideforming core material can beaccomplished simply by diffusing carbon thereinto from the outer layersof high carbon steel which is thereby depleted of carbon, resulting in afinal product comprising low carbon exterior layers enclosing an innerlayer having the thus-formed carbides dispersed therein.

Still other materials are useful as outer layers in the initiallaminate, e.g., various stainless steels, other ironbase alloys, orsofter metals, as copper, tin, zinc, etc., or alloys thereof.

On occasion, it may be desirable to assemble the initial laminatedarticle'in the form of an enclosed, evacuable pack for subsequenttreatment and rolling, as aforesaid. In such instances, the readilyworkable, outer laminations may comprisethe pack exterior, enclosing theinner lamination of the stable carbide-forming metal, and sealing may beaccomplished by edge welding in accordance with well-known techniques ofthe prior art. The pack, so constituted, may be evacuated, or may besupplied with an atmosphere of a suitable inert gas, as argon, etc. Thepurpose of such constructions and procedures is, of course, to avoidoxidation of the stable carbide forming metal of the inner laminationwith consequent tendency of the final product to delarninate readily.

Alternatively, thecontemplated articles may be produced from a unitarystock. For example, a low carbon iron-base alloy, as, one of thecommercial cold-rollable stainless steels, for example, AISI 430 (0.12%C), or a low carbon steel, as AISI 1010, or any other relatively readilyrollable, low carbon iron-base alloy. Such alloys which, in accordancewith the common knowledge of the prior art, are most readily coldrollable, are preferred as initial starting material. Pursuant to thisaspect of the invention, metal stock, as aforesaid, is rolled topenultimate thickness, whereupon it is carburized as aforesaid.Carburization is carried out to any desired extent, but is preferablylimited to less than complete saturation of the metal with carbon, toavoid complete embrittlement of the metal, which would make handlingthereof extremely difficult. The carburized metal is then subjected to adiffusion annealing treatment for a time and at a temperature suflicientto produce substantial homogeneity of carbon throughout the metal. Theincreased carbon content, of course, results in a considerably enhancedhardness of the metal, thereby making the same more suitable for cuttingapplications than the unhardened, low carbon raw material. Moreover, inthe case of metals containing carbide-forming elements, as chromium,vanadium, molybdenum, tungsten, etc., interaction thereof with carbonduring the aforesaid treatment is also productive of the correspondingmetallic carbides which also contribute to the cutting ability of thefinal product. However, the increased hardness due to higher carboncontents is accompanied by a decrease in ductility and toughness of themetal, which makes rolling and other fabricating steps quite difiicult.Indeed, as described above, it is such factors which commonly precludeuse of high hardness metals in the manufacturing of thin gauge cuttingtools as razor blades and the like.

However, it has now been found possible to utilize such high hardnessmaterials, prepared as above described, by subjecting the same to asurface decarburization step, whereby carbon in the surface layers ofthe carburized, annealed stock, is reduced to a level conducive to coldrolling, e.g., to a carbon level about that present in the initial,untreated stock. The result, then, is a unitary stock of base metal,having a relatively higher carbon, high hardness, central core, eitherwith or without metallic carbides, as aforesaid, integral withoverlying, exterior layers of relatively lower carbon base metal whichexhibit properties of higher ductility, toughness and workability thanthe core layer. Consequently, the surface decarburized metal may then bereadily cold rolled to a final desired thickness. The highly workableexterior layers effectively support the higher hardness central core andthereby enable the mechanical reduction thereof to the desired, finalthickness without danger of cracking or breaking. The thus-producedstock is then cut, by suitable means, to form blanks of a desiredarticle form.

Illustrative of the aspect of the invention as above described, AISI 430stainless steel, a ferritic steel comprising 0.12% carbon, 1.00%manganese, 0.040% phosphorous, 0.03% sulphur, 1.00% silicon, 14 to 18%chromium, balance substantially iron, was rolled to a thickness of 10mils and the rolled material was then carburized in an atmosphere ofnatural gas containing a small percentage of oxygen sufficient todeposit a thin film of carbon on the steel surface. The carburizationstep was carried out at 1800 F for a period of two hours. The carburizedarticle was thereafter diffusion annealed in a vacuum at a temperatureof 1800 F. for a period of three hours whereupon the carbon content ofthe article was substantially uniformly diffused therethrough. Thecarburized and annealed article was then subjected to a partialdecarburization in wet hydrogen (70 F. dew point), at 1800 F. for onehour. Examination of the decarburized product showed top and bottomlayers approximately 3 to 4 mils thick wherein decarburization hadreduced the carbon content to essentially that of untreated 430stainless steel, and a central layer from 2 to 4 mils in thickness ofrelatively high carbon content, i.e., about one weight percent carbon.The decarburized product was then cold rolled to a final thickness ofsix mils. It was found, upon examination of sections of the finalcomposite metal stock that the same comprised a central layer or coreabout 0.0015 inch thick of a transformed austenitic structure having arelatively much higher carbon content than the adjacent, outer layers,each of which measured 0.0023 inch in thickness, although there were nosharply defined boundary layers separating the high carbon interior fromthe low carbon surface material. The core layer, by reason of itstransformed austenitic structure, and because of its higher carboncontent, was inherently much harder, and hence more suitable for cuttingand wear resistance, than the lower carbon outer layers.

The invention is not limited to the above-mentioned illustrativearticles, but is applicable to a wide variety of products and methods ofmaking the same. Thus, the invention is useable with great advantage inthe production of a wide variety of other cutting tools, as machinecutting tools, tool bits, agricultural discs and the like, as well asarticles and stock as structural articles, etc., wherein a highhardness, delamination-resistance core is useful or required.

Manifestly, still further modifications and additions may be made to theabove-mentioned descriptive and illustrative matter without departingfrom the spirit and scope of the invention.

What is claimed is:

1. A method of producing flat metal articles for cutting blades,comprising forming a laminated stock consisting of an inner layercomprising a strong carbide-forming metal and outer layers comprising amechanically workable, matrix metal having substantial solid solubilityfor carbon and forming therewith carbides relatively less stable thanthose formed by the strong carbide-forming metal of the inner layer,heating the laminated stock to diffuse the carbide-forming metal of theinner layer into adjacent portions of the outer layers, carburizing thestock, annealing the carburized stock to effect diffusion of carbontherethrough and to form a centrally disposed, discrete, interior layerof matrix metal containing a substantially homogeneous dispersion ofstable carbides, partially decarburizing the stock to substantiallyeliminate the relatively more unstable carbides and dissolved carbon andto restore the outer layers of matrix metal to a mechanically workablecondition, and rolling the stock to a desired, final article thickness.

2. A method of making flat-rolled mill articles comprising a matrix of arelatively ductile, workable metal and a continuous, centrally disposed,inner layer containing dispersed carbide particles adapted to form acutting edge, comprising forming a laminated stock consisting of aninner lamination of a relatively active metal capable of forming stablecarbides and juxtaposed outer laminations of a rollable matrix metalcapable of forming carbides relatively less stable than those of saidreactive metal, diffusion alloying the reactive metal and adjacentportions of the matrix metal to form an inner alloy layer of matrixmetal and reactive metal, carburizing the stock to form reactive metalcarbides in the inner layer, decarburizing the outer laminations of thestock, and rolling the stock to a desired final article thickness.

3. A method of producing flat-rolled metal articles comprising a hard,wear-resistant, inner layer capable of forming a cutting edge and outerlayers of a relatively ductile, workable metal, comprising interposingbetween outer layers of the workable metal a layer comprising a stablecarbide-forming metal, diffusing carbon through the outer layers toreact with the stable carbide-forming metal to form a dispersion ofstable carbides in a matrix of the workable metal, decarburizing theouter layers of workable metal, and working the resulting product to adesired final article form.

4. A method for making flat-rolled mill stock comprising forming a packconsisting of an inner lamination of a strong carbide-forming metal andjuxtaposed outer laminations of a rollable metal forming carbidesrelatively less stable than those of the strong carbide-forming metal,excluding air from the pack, diffusing the inner lamination intoadjacent portions of the outer laminations, carburizing the pack to forman inner layer containing substantially uniformly dispersed stablecarbides, partially decarburizing the pack, and rolling the pack to adesired final thickness.

5. A method of making a cutting tool having a relatively hard,wear-resistant inner layer constituting a cutting edge and relativelysofter, ductile, outer layers, comprising interposing between stocklaminations of the softer, more ductile metal, a lamination comprising astable carbide-forming metal, carburizing the laminated stock to formstable carbides in a zone corresponding to the interposed lamination,decarburizing the outer laminations, rolling the carbide-containingstock to a desired final thickness, forming cutting tool blanks from therolled stock, and double bevel grinding at least one edge of the blankto expose the inner, carbide-containing layer to form a cutting edge.

6. A method for producing a metal article having a core of high hardnessand relatively softer overlying layers comprising: forming a metalcomposite having a central zone of a strong carbide-forming metal,producing thereover a high-carbon outer zone of metal having asubstantially higher carbon content than said strong carbide-formingmetal, annealing said composite to diffuse carbon throughout saidcomposite to form within said central zone discontinuous, homogeneouslydispersed carbide particles of said carbide-forming metal, andsubjecting said composite to a decarburiz/ing treatment to remove atleast a portion of the carbon from the outer zone thereof.

7. A method according to claim 6 wherein said highcarbon outer zone isproduced by carburizing said composite to increase the carbon content ofthe metal of said outer zone to a level substantialy higher than thecarbon content of the metal of said central zone.

8. A method according to claim 7, wherein said composite is cold reducedto a final thickness after decarburization.

9. A method according to claim 8, wherein said composite is deoxidizedafter decarburization.

10. A method according to claim 9, wherein said composite is deoxidizedby annealing at a temperature between about 1500 F. and 2000 F., at apressure below about 50 microns Hg, and for a time of at least fiveminutes, whereby internal oxidation of said composite is removed to adepth of about 1 mil.

11. A method according to claim 6, wherein portions of said central-zonemetal and said outer-zone metal are alloyed along the interfacesthereof.

12. A composite metal article produced in accordance with the method ofclaim 6.

References Cited by the Examiner UNITED STATES PATENTS 2,531,731 11/1950Hibbert 148-12.1 X 3,109,877 11/1963 Wilson 148-16 OTHER REFERENCESSteel Processing, May 1944, pp. 302-306.

HYLAND BIZOT, Primary Examiner. DAVID L. RECK, Examiner. H. F. SAITO,Assistant Examiner.

1. A METHOD OF PRODUCING FLAT METAL ARTICLES FOR CUTTING BLADES,COMPRISING FORMING A LAMINATED STOCK CONSISTING OF AN INNER LAYERCOMPRISING A STRONG CARBIDE-FORMING METAL AND OUTER LAYERS COMPRISING AMECHANICALLY WORKABLE, MATRIX METAL HAVING SUBSTANTIAL SOLID SOLUBILITYFOR CARBON AND FORMING THEREWITH CARBIDES RELATIVELY LESS STABLE THANTHOSE FORMED BY THE STRONG CARBIDE-FORMING METAL OF THE INNER LAYER,HEATING THE LAMINATED STOCK TO DIFFUSE THE CARBIDE-FORMING METAL OF THEINNER LAYER INTO ADJACENT PORTIONS OF THE OUTER LAYERS, CARBURIZING THESTOCK, ANNEALING THE CARBURIZED STOCK TO EFFECT DIFFUSION OF CARBONTHERETHROUGH AND TO FORM A CENTRALLY DISPOSED, DISCRETE, INTERIOR LAYEROF MATRIX METAL CONTAINING A SUBSTANTIALLY HOMOGENEOUS DISPERSION OFSTABLE CARBIDES, PARTIALLY DECARBURIZING THE STOCK TO SUBSTANTIALLYELIMINATE THE RELATIVELY MORE UNSTABLE CARBIDES AND DISSOLVED CARBON ANDTO RESTORE THE OUTER LAYERS OF MATRIX METAL TO A MECHANICALLY WORKABLECONDITION, AND ROLLING THE STOCK TO A DESIRED, FINAL ARTICLE THICKNESS.